The present invention relates generally to subterranean treatment operations, and more particularly to methods of completing and stimulating a well bore.
In the oil and gas industry, a common step in the completion of a well bore is to cement pipe strings, such as casings and liners, in the well bore. Generally, a well bore is drilled and a pipe string is inserted into the well bore. A cement composition is then pumped into the annular space between the walls of the well bore and the exterior surface of a pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement that substantially supports and positions the pipe string in the well bore, and that bonds the exterior surface of the pipe string to the walls of the well bore. Cements that are typically used in subterranean cementing operations are substantially impermeable, in all areas outside of the perforated interval.
After a well bore has been drilled and the pipe string has been cemented, it is also common to perform one or more subsequent completion and/or stimulation operations, including, but not limited to, hydraulic fracturing and sand control treatments. Hydraulic fracturing operations generally involve pumping a treatment fluid (e.g., a fracturing fluid) into a well bore that penetrates a subterranean formation at a sufficient hydraulic pressure to create or enhance one or more cracks, or fractures, in the subterranean formation. “Enhancing” one or more fractures in a subterranean formation, as that term is used herein, is defined to include the extension or enlargement of one or more natural or previously created fractures in the subterranean formation. The treatment fluid may comprise particulates, often referred to as proppant particulates, that are deposited in the fractures. The proppant particulates, inter alia, may prevent the fractures from fully closing upon the release of hydraulic pressure, forming conductive channels through which fluids may flow to the well bore. The proppant particulates also may be coated with certain types of materials, including resins, tackifying agents, and the like, among other purposes, to enhance conductivity (e.g., fluid flow) through the fractures in which they reside.
One common type of sand control treatment is gravel packing. Typical gravel packing treatments involve suspending particulates (commonly referred to as gravel particulates) in a treatment fluid, and depositing at least a portion of those particulates in a desired area in a well bore, e.g., near unconsolidated or weakly consolidated formation zones, to form a gravel pack. In general, a gravel pack is a grouping of particulates that are packed sufficiently close together so as to prevent the passage of certain materials through the gravel pack. This gravel pack may, inter alia, enhance sand control in the subterranean formation and/or prevent the flow of particulates from an unconsolidated portion of the subterranean formation (e.g., a propped fracture) into a well bore. One common type of gravel-packing operation involves placing a sand control screen in the well bore and packing the annulus between the screen and the well bore with the gravel particulates of a specific size designed to prevent the passage of formation sand. The gravel particulates act, inter alia, to prevent the formation sand from occluding the screen or migrating with the produced hydrocarbons, and the screen acts, inter alia, to prevent the particulates from entering the well bore. The gravel particulates may also be coated with certain types of materials, including resins, tackifying agents, and the like, among other purposes, to enhance conductivity (e.g., fluid flow) through the gravel pack in which they reside. In some situations, fracturing and gravel-packing treatments are combined into a single treatment. These combined treatments may be commercially available under the trade name FRAC PAC™ from Halliburton Energy Services, Inc. of Duncan, Okla. In such combined treatments, the treatments are generally completed with a gravel pack screen assembly in place with the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In this situation, the hydraulic fracturing treatment ends in a screen-out condition, creating an annular gravel pack between the screen and casing. In other cases, the fracturing treatment may be performed prior to installing the screen and placing a gravel pack.
In traditional well bores, installing and cementing pipe strings, as well as performing subsequent operations such as hydraulic fracturing and sand control treatments, may be costly and time consuming. The cost and complexity of traditional completion, stimulation, and sand control techniques, including installing casings, performing cementing, installing sand control screens and performing gravel packing, may be even greater in slim hole well bores. As used herein, the term “slim hole well bore” refers to a well bore that is about five inches in diameter or less. Slim hole well bores may be substantially vertical, high deviated, or horizontal. In some hydrocarbon recovery operations it may be preferable to drill a slim hole well bore rather than a traditional well bore. Among the many potential advantages of drilling a slim hole well bore are the typically shorter drilling times, the ability to use less-bulky drilling equipment, the creation of fewer drill cuttings, and the reduced drill cutting disposal costs arising from the reduction in drill cuttings. In some cases, the cost savings associated with drilling a slim hole well bore may be negated by the increased cost of cementing the slim hole well bore. As a result, some sections of a well bore may be left in an openhole condition. As used herein, the term “openhole” refers to a well bore that comprises at least one section that does not comprise a casing string. The term “openhole section” is used herein to refer to a section of a well bore that does not comprise a cemented casing string. At times, an openhole well bore may comprise an openhole section that is completed with stand-alone screen completions using slotted liners, wire-wrapped screens, premium screens, or expandable screens in addition to the use of gravel pack completions.
Because of well bore size restriction, performing gravel packing or frac-packing completions in slim holes may be challenging and costly. Frequently, open holes of long horizontal well bores, even those of conventional bore sizes (not slim holes), are completed with sand alone screens because of cost and complexity involved with gravel packing or other sand control methods.